Tele Vue have not specifically endorsed the 13mm Ethos for Bino-Vue use because of the large diameter barrel. Even so, they were advised by Mike Harvey at the Winter Star Party (February 2008) that only 1-person in 25 had interpupilary limits with the bino'd Ethos (63.5-mm for the initial production 13mm).

However, since many customers have been thrilled with the experience, Tele Vue have maximized the potential use by narrowing the barrel from 63.5-mm to 62-mm diameter for eyepieces delivered beginning mid-March 2008. While the difference is only 1.5-mm, (or 0.75-mm for pairing a first production unit with current production) they decided to make this small change public, in case you want to give it a try.